1. Field of the Invention
This invention relates to an ink used in ink-jet recording in which ink droplets are ejected from a recording head by the action of thermal energy to record images on a recording medium, and an ink jet recording method making use of such an ink. More particularly, this invention relates to an ink which can improve ejection stability of inks making use of pigments as coloring materials and can achieve a high fastness when images are recorded using the ink, and an ink jet recording method making use of such an ink.
2. Description of the Related Art
Various systems have conventionally been proposed in the printing that employs an ink jet recording method. Of these, for example, an ink jet recording method disclosed in Japanese Patent Application Laid-open No. S54-51837 in which ink is ejected in the form of ink droplets by the action of thermal energy (what is called a BUBBLE JET (registered trademark of CANON INC.) process) facilitates a high-density multi-nozzle very much. Hence, this process has characteristic features that high-quality images are obtainable at a high speed and at a very low cost, and that images are printable also on plain paper, which does not have any special coating layer. In this recording process, a heater of the recording head is rapidly heated, whereupon a liquid on the heater comes into air bubbles to cause an abrupt increase in volume. In virtue of the force of action standing on this abrupt increase in volume, ink droplets are ejected from nozzles at the tip of the recording head and fly therefrom to the recording medium to adhere thereto, thus printing is performed.
In such an ink jet recording method, it is usual to use aqueous dye inks. Recently, however, it has come to be attempted to use aqueous pigment inks in the ink-jet recording. The reason therefor is that the latter is the best material that can give fastness such as water resistance or light-fastness to images formed using the aqueous pigment inks. As to such aqueous pigment inks, ink-jet recording aqueous pigment inks satisfying basic properties such as image recording quality level, ink ejection performance, storage stability, anti-clogging and fixability are disclosed in, e.g., Japanese Patent Applications Laid-open Nos. H02-255875, H04-334870, H04-057859 and H04-057860.
However, as a problem that may arise when an aqueous pigment ink is ejected by the BUBBLE JET (registered trademark) process, it comes about that the ink is exposed to high temperature at the heater surface of the recording head. The BUBBLE JET (registered trademark) process is greatly characterized in its possibility for higher nozzle density, and is superior in this regard. However, components contained in the pigment ink may change in properties because of an effect due to the high temperature at the heater surface of the recording head to become accumulated on the heating element surface as deposits. With accumulation of such deposits, it may come about that the heater of the recording head comes to have, at its surface, poorer heat conduction performance with time, so that the impact pressure accompanying the bubbling of ink becomes lower, resulting in a deterioration of ejection performance, and furthermore resulting in a poor quality of recorded images.